Preheat and prep: Heat your oven to 425°F (220°C). Line a sheet pan with parchment for easy cleanup.
Season the chicken: Pat chicken dry with paper towels.
Toss with olive oil, salt, pepper, garlic powder, paprika, and oregano until evenly coated.
Roast: Arrange chicken in a single layer. Roast for 18–22 minutes for breasts or 20–25 minutes for thighs, until the internal temperature reaches 165°F (74°C) and the edges are slightly browned.
Rest and slice: Let chicken rest for 5–10 minutes, then slice or cube into bite-size pieces. Resting keeps the meat juicy.
Make the dressing: In a small bowl or jar, whisk together olive oil, lemon juice, Dijon, honey, garlic, salt, and pepper until emulsified.
Taste and adjust salt, pepper, or lemon as needed.
Build the salad base: In a large bowl, add mixed greens, tomatoes, cucumber, red onion, and herbs. Drizzle about half the dressing and toss gently to coat.
Add the chicken and toppings: Top with warm or cooled chicken, avocado, nuts, and cheese if using. Spoon over more dressing to taste.
Finish and serve: Toss lightly one last time.
Serve immediately for warm chicken salad, or chill for 20 minutes for a refreshing cold version.